Simplify $2w+4w+6w+8w+10w+12$.
Solution: We have to be careful!  We can combine all the $w$ terms to get \[2w+4w+6w+8w+10w+12 = (2+4+6+8+10)w + 12 = \boxed{30w+12},\] but we can't combine the 12 with anything!